U.S. Pat. No. 5,370,504 issued to Nagashima on Oct. 12, 1993 discloses an ambulant reciprocating compressor having plural pressure collection chambers. A pair of oppositely directed pistons is mounted in a cylinder in a reciprocating manner. The cylinder is formed unilaterally with, and is encapsulated within, a tank for receiving compressed air and has an exhaust port at each end and a valve for controlling the flow of air into the tank. Each piston has a head with an aperture and a unidirectional valve for controlling air flow into the cylinder. An air inlet to the cylinder is located between the piston heads. A motor which has a drive shaft extending through the air inlet and a transmission connected to the pistons drives the pistons synchronously in opposing, reciprocating strokes. The compressor of this patent produces less noise caused by vibration because there is no piping in the apparatus and the fittings and attachments for the compressor are all installed inside the body. The apparatus of the patent fails to decrease noise as fully as desired. The essentially solid wall adjacent the outlet valve reflects noise back out the intake opening and there is no noise protector at the intake opening.
U.S. Pat. No. 6,099,268 issued to Pressel on Aug. 8, 2000 represents the closest prior art known by the inventor. This patent discloses an air compressor system which is characterized by being made up of a swash plate type of air compressor which is capable of delivering pressures up to about 200 p.s.i. The system is selectively and interchangeably insertable into holding tanks of different sizes and configurations for different specific applications. The holding tanks have inner tank liners and a connecting valve between the compressor and liner to deliver pressurized air from the compressor into the storage compartment defined by the liner within the tank. The tank and its liner can serve as a self-contained source of pressurized air which can be selectively discharged as required so that the compressor itself may be disconnected from the tank and successively connected to a number of different or additional tanks. This patent is concerned with noise reduction in a system containing a tank, a motor and a pneumatic compressor. Noise is reduced by a muffler sleeve on the tank liner, a plurality of baffle ports which allow air into the liner, curved vanes in the bottom of the tank liner, and vibration-dampening attachment bolts. This system is partially effective for its intended purpose. However, there is room for improvements. The tank assembly has a closed bottom which acts as a sounding board to reflect noise upward and into the environment. Additionally, the top of the compressor assembly is covered by a screen which offers no resistance to noise produced by the compressor being transmitted to the environment.
U.S. Pat. No. 6,361,293 issued to Harper on Mar. 26, 2002 discloses a hermetic compressor which includes a housing and a compressor subassembly resiliently supported within the housing. The compressor subassembly includes a motor drivingly coupled to a compressor mechanism by means of a shaft. A motor enclosure is connected to the compressor mechanism and encases the motor. A pair of grommets is disposed between the housing and the compressor subassembly whereby the compressor subassembly is resiliently suspended within the housing. The compressor mechanism discharges compressed gas into the housing through an aperture located in the motor enclosure and a quantity of oil is disposed in a lower portion of the housing. The aperture is submerged in the quantity of oil and the discharge gas exiting through the aperture is urged through the quantity of oil forming a sound damping foam. A main bearing is connected to the motor enclosure. A first discharge chamber is defined by the main bearing and the inner surface of the motor enclosure and a second discharge chamber is defined by the inner surface of the housing and an outer surface of the compressor subassembly. The first and second discharge chambers constitute a pair of mufflers to consecutively receive a quantity of discharge gas and respectively muffle the gas being respectively discharged therefrom. A method of assembling the rotary compressor includes inserting a mounting tool into a hole in the projecting portion of the motor enclosure and aligning a stator-rotor air gap prior to assembling the compressor subassembly within resilient mounts attached to the housing. When the air emitted from the device of this invention is to used for inhalation by humans, such as in the well-known CPAP machine, the passage of the air through oil may produce air bearing harmful droplets of oil and thus be unsatisfactory for its intended purpose. Additionally, the incorporation of additional heavy oil is not desirable in the production of portable compressor devices.
U.S. Pat. No. 2,964,236 issued to Kasper on Dec. 19, 1960 discloses a suction motor mounting construction. A suction cleaner has a motor mounted within a tank. The device of Kasper is a vacuum cleaner in which air is forced by a fan through a filter to remove solid particles. There is no apparent consideration of noise reduction in this disclosure.
U.S. Pat. No. 4,964,609 issued to Tomell on Oct. 23, 1990 discloses a vertically upright hermetic compressor for mounting to a horizontal support surface, having a housing, a motor compressor unit within the housing, and a mounting piece. The object of the Tomell invention is to diminish undesirable noise emanating from the bottom of the compressor units. To accomplish this object, the mounting piece is removably attached to the housing's bottom end for mounting the compressor to the horizontal support surface. It has a resilient body engaged about the housing to cover the housing bottom. While effective for its purpose, the Tomell device is only partially effective in producing a quiet motor/compressor, and there is considerable room for improvement in this area.
U.S. Pat. No. 4,961,018 issued to Akhter on Oct. 2, 1990 discloses an enclosed pump motor includes an aluminum housing made by an impact extrusion process. The housing is cylindrical having an integrally-formed closed end with integral fastener bosses for attaching a pump thereto and an integrally-formed thickened cylindrical portion defining a shaft bore for receiving the motor shaft. At the other end, the cylindrical housing is open for receiving the motor. A motor cover is attached to the motor receiving end of the housing by crimping or bending a part of the housing into indents formed in the housing. The motor cover includes a threaded bore adapted to receive a threaded grommet wherein three connector pins are imbedded. The connector pins are connected to electrical power carrying conductors and/or switch conductors leading to a fluid level sensor switch. The conductor-to-pin connections are imbedded within the grommet and are hermetically sealed. The connector pins extend into the housing and are electrically connected to corresponding connectors leading to the electric motor. The motor is enclosed within a housing which is in direct contact with surrounding environment. No effort is made to reduce the noise generated by the motor or pump.
U.S. Pat. No. 6,447,264 issued to Lucas on Sep. 10, 2002 discloses a compressor system having a first compartment for housing relatively quietly operating equipment, and a second compartment for housing relatively noisily operating equipment. The second compartment is substantially closed off from the surrounding atmosphere to reduce the amount of noise that can be heard outside the compressor system on account of the noisy equipment operating within the compressor system housing. The second compartment includes a small air inlet opening and a small air outlet opening to allow enough air to flow through the second compartment to cool the equipment housed therein. The small openings reduce the amount of airborne noise which is released to the outside environment. The compressor system also has an air intake directing device for directing an appropriate amount of air into the second compartment to cool the noise generating machinery located within the second compartment, and for directing an appropriate amount of air to an air inlet opening of a compressor, thereby more efficiently using the air drawn into the compressor system housing. By separating the several parts of the system, Lucas creates a system which is larger than necessary. In the preparation of portable devices, this is disadvantageous. There is no provision for preventing the noise generated by the relatively noisy components from being transmitted to the environment through the intake opening.
Patent application number US2002/0009372A1 by Gruber published on Jan. 24, 2002 discloses an air compressor assembly with a shroud. An apparatus comprises a tank, an air compressor, and a motor with an output shaft. A fan is mounted on the output shaft. A drive assembly interconnects the motor operatively with the compressor. The apparatus further includes a base structure and a shroud. The base structure is configured to support the compressor, the motor and the drive assembly on the tank. The shroud is configured to cover the compressor, the motor, the drive assembly and the base structure on the tank. The shroud has a cooling air inlet port and a cooling air outlet port. A plurality of internal wall portions of the shroud are configured to direct cooling air to flow over the motor and the compressor upon flowing through the cover from the inlet port to the outlet port under the influence of the fan. The fact that the tank supports the operational components means that the apparatus is larger than it should be which is a disadvantage in portable apparatuses.
U.S. Pat. No. 6,308,899 issued to Crofford on Oct. 30, 2001 discloses a compact, highly portable, multi-mode fluid injection system able to reach difficult-to-access places to efficiently service pipes, tubing and related components having a variety of diameters. The system comprises a tank having a first port which allows access to the tank's upper contents and a second port which allows access to the tank's lower contents, a means for introducing liquid into the tank, a hand pump built into the tank to pressurize the tank and its contents, one or more applicators, and flexible hoses which connect the applicators to the first and/or second port to supply the applicators with the tank's contents. The system is capable of producing, alternatively, pressurized liquid or gas without an independently powered air compressor or consumable gas cartridges, and without having to empty and/or fill the tank. An onboard means for stowing the hose conduits, and injection gun applicator having a small travel high-flow valve with adjustable accumulation chamber, and applicators having stiff-flexible tips and tip extensions is disclosed. This system does not contain a motor or a compressor, and is not concerned with noise abatement.
As can be seen from the above-discussed publications, noise produced by air compressors is a persistent problem. Operators of pneumatic equipment are forced to wear ear protectors or risk hearing loss due to noisy conditions which exceed OSHA standards. In spite of the recognition of this problem and the various approaches to solve this problem, the noise produced by fluid compressors still exists.